[cros] Default user picture is chosen randomly.
[cros] Default user picture is chosen randomly.

BUG=chromium-os:19811
TEST=Manual: enable WebUI and create a new user. Each time a random picture should be selected by default.


Review URL: http://codereview.chromium.org/7790025

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@98819 0039d316-1c4b-4281-b951-d872f2087c98

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